Chapter 9: Thermal Properties of Matter

Question 1

Internal energy

Answer 1

The total energy of all the particles in the substance
Joule (J)

Internal potential energy
Internal kinetic energy

Question 2

Internal potential energy and kinetic energy

Answer 2

INTERNAL POTENTIAL ENERGY 
The forces between the particles
How far apart they are
INTERNAL KINETIC ENERGY 
Directly related to temperature

Question 3

Solidification

Answer 3

Freezing

Question 4

Boiling / Evaporation

Answer 4

Occurs at boiling temperature / Occurs below the boiling temperature
Occurs rapidly / Occurs slowly
Occurs throughout the liquid / Occurs only at the surface of the liquid
Bubbles form / No bubbles form
Temperature remains constant / Temperature may change
External energy source needed / External energy source not needed

Question 5

Factors affecting the rate of evaporation

Answer 5

1. Temperature 
Higher temperature, faster evaporation 
2. Surface area 
Greater surface area, faster evaporation 
3. Movement of air 
The presence of air, faster evaporation 
4. Humidity
The more humid, slower evaporation 
5. Pressure
The greater the pressure, slower evaporation 
6. Boiling point of liquid 
The lower the boiling point, faster evaporation

Question 6

Why evaporation cause cooling?

Answer 6

Molecules in the liquid absorb thermal energy from the surroundings. At the liquid surface, molecules that are more energetic can overcome the attractive forces of other molecules and escape into the atmosphere. The slower moving molecules left behind are less energetic. This lowers the temperature of the liquid